The present invention relates to electronics system configurations, particularly those that use removable circuit board modules using a clamping mechanism known commonly as circuit board retainers or card retainers and that are required to pass stringent shock and vibration requirements.
Many harsh environment electronics systems, such as computer and telecommunications systems, are designed to use replaceable electronic circuit boards, sometimes referred to as Line Replaceable Units (LRUs). An LRU is a modular circuit board that is designed to plug into a chassis and electrically connect to other LRU boards via a backplane in the chassis. Typically, a given chassis is designed to hold multiple LRUs. In general LRUs must comply with pre-determined specifications so that modules provided by various manufacturers may be readily used in combination. Example standards are, but are not limited to, VME, VME 64, cPCI, ATCA, AMC, ARINC, and MicroTCA, with these standards being defined by several organizations including ANSI, PICMG, IEEE, VITA, and other standards organizations.
Electronics systems for extreme environments rely on LRUs that are designed for high shock and vibration. Further, because these modules contain electronics that generate heat, a suitable method to dissipate heat efficiently is desired. To achieve thermal and structural performance, a clamping device known as a card retainer is employed to secure the LRU to the chassis and, in the case of conduction cooling, to provide a thermal pathway to dissipate heat from the module to the walls of the chassis enclosure.
It is common for these standards to require that the LRUs are removable and are typically inserted perpendicular to the chassis walls. Once the LRU is inserted, a card retainer is employed to secure the LRU to the chassis wall. In addition to providing a clamping mechanism to retain the module, a card retainer in a conduction cooled application can also provide an efficient method of transmitting thermal energy from the module to the walls of the enclosure.
Typically card retainers use a series of ramps or wedges that are forced to slide onto one another to clamp the LRU to the chassis. The wedges slide onto one another at an acute angle, typically at 45°. The action of the wedges sliding one above the next create an expansion of effective height of the total assembly which creates a frictional force that holds the LRU in place and creates a conductive path, for conduction cooled applications, for the thermal energy from the LRU.
In the prior art, the card retainer employs a central support member consisting of a long bar, a screw, or a shaft that connects and aligns all wedges. For example, see U.S. Pat. Nos. 4,819,713; 4,823,951; and 5,485,353. A screw or lever then can apply linear force to the aligned wedge segments to force the wedges towards one another converting horizontal force to vertical force. The supporting member or shaft that connects all of the wedges to one another is typically positioned through the center of all of the wedges.
While the above arrangements have proven satisfactory for many situations, they may be less than satisfactory for others, particularly for high heat load situations. As such, there remains a need for alternative approaches for more efficient cooling and better structural clamping force to retain the LRUs.